Fluid valves control the flow of fluid from one location to another. When the fluid valve is in a closed position, high pressure fluid on one side is prevented from flowing to a lower pressure location on the other side of the valve. The pressure differences between an inlet and an outlet of the control valve, along with a tortuous flow path through the control valve, produce turbulent fluid flow downstream of the control valve, which causes unwanted and potentially harmful noise.
In an attempt to reduce noise, multi-port cages or trims have been used in some regulators to reduce the pressure drop across the cage and to smooth downstream flow. However, these cage-type noise reducers also reduce fluid flow rates through the cage, which may reduce efficiency of the regulator.
Other types of sound reducing devices include materials disposed in the flow path that absorb sound waves and convert the sound waves to heat energy. However, such sound absorbing materials have limited effective frequencies and they also reduce fluid flow through the material.
Still other attempts have been made to reduce noise with attenuation devices located downstream of the regulator. In particular, a modal coincidence suppression device is described in “The Modal Coincidence Suppression Device (MCSD) For The Reduction Of Noise From Control Valves” by Ali E. Broukhiyan, hereinafter (“MCSD”) which is hereby incorporated by reference herein. However, the modal suppression device disclosed in MCSD was very heavy and was difficult to assemble.